A common metal welding technique employs the heat generated by electrical arcing to transition a portion of a workpiece to a molten state, and the addition of filler metal from a welding wire. One technique that employs this arcing principle is wire-feed welding. Wire-feed welding involves routing welding current from a power source into an electrode that is brought into close proximity or contact with the workpiece. In typical wire-feed systems, electrode welding wire is directed through a welding cable, into a torch assembly, and particularly into a contact tip mounted to the torch assembly. Electrical current is routed from the welding cable to the welding wire through the contact tip. When a trigger on the welding torch is operated or an “on” signal is assigned by a robot/automatic controller, welding wire is advanced toward the contact tip, at which point current is conducted from the contact tip into the egressing welding wire. When the welding wire is sufficiently close to or touching the workpiece, current arcs from the welding wire to the workpiece, completing a circuit and generating sufficient heat to melt and weld the workpiece. Often, the welding wire is consumed and becomes part of the weld itself. Thus, new welding wire is advanced, continuously replacing the consumed welding wire and maintaining the welding arc. One common type of wire-feed welding is metal inert gas (“MIG”) welding.
The use of high strength, low alloy steels has encouraged the development and application of new gas metal arc welding (“GMAW”) processes such as pulse processes and modified short circuit processes. When welding thin sheet metal at a high speed, the welding arc is typically controlled to be “short, tight, and stiff,” which corresponds to a low energy input. When a contact tip of a MIG torch is used and deteriorated, the energy transfer efficiency decreases. This results in lower energy (or voltage) being consumed at the arc. When the energy consumption is too low to maintain a smooth welding arc, stubbing occurs, which causes defects such as cold welding and discontinuous beads.
Increasing the contact force between the welding wire and the contact tip helps to ensure proper energy transfer efficiency. Two conventional methods to increase the contact force are increasing the wire cast (the curvature) through the use of a special jump liner inside the gooseneck, and bending the wire against the contact tip.
However, if the wire cast is too tight, the portion of wire that sticks out of the contact tip, between the contact tip and the arc, is significantly curved, causing misalignment issues. From a standpoint of application of the welding wire, it is desirable to have as straight a contour of welding wire as possible fed out of the contact tip. Hence, for a conventional MIG torch, improving the contact force and achieving straight wire contour are a pair of factors that are very difficult to balance.
Another factor that affects welding quality is wire twist. Due to the moving/rotating of a welding torch, the welding wire may flip or twist inside of the torch. This causes a sudden change in the contacting point between the welding wire and contact tip, and correspondingly causes fluctuation of the welding current and welding quality. It has been shown that the abovementioned method of bending the wire against the contact tip causes noticeable current fluctuation, especially when the wire cast is tight.
Therefore, a need exists for an improved assembly and method for controlling welding wire to achieve straight contour when the welding wire is fed out of a contact tip of a welding torch, and for maintaining sufficient contact force at a consistent point in the contact tip.